Home networking explained, Part 8: Cable modem shopping tips

CNET editor Dong Ngo shares tips on how to best equip your home for cable Internet while saving your hard-earned dollars.

The back on a typical DOCSIS 3.0 cable modem. Note the LAN port (top) and the coaxial port.

Editors' note: This post is part of an ongoing series. For the other parts, check out the related stories section below.

If you're looking for the best home broadband speeds, cable Internet service is still the go-to choice for most users. But what many people don't know is that they may be paying more than they need to for cable broadband -- especially if they use the equipment provided by the cable company.

Related stories:

Part 1: Basic terms

Part 2: Optimizing your Wi-Fi network

Part 3: Taking control of your wires

Part 4: Wi-Fi vs. Internet

Part 5: Setting up a home router

Part 6: Securing your network

Part 7: Power line explained

Indeed, many users can save upward of $7 per month -- more than $80 per year -- on their current cable Internet service. To that end, I've boiled down the five most popular reader questions I generally receive on the subject of cable Internet. I've included short and more in-depth answers to each, including suggestions on how to save on your monthly bill (spoiler: buy, don't rent, your cable modem).

Whether you're a current cable Internet customer or you're thinking of switching, this Q&A should set you up to get the biggest bang for your broadband buck.

What cable modem should I get?

The short answer:
Get one that's capable of delivering at least the speed of the broadband data plan to which you subscribe. When in doubt, get one that supports DOCSIS 3.0. Of those, get the cheapest one that's on your cable provider's approved list; examples of such lists are this list from Comcast and this one from Time Warner Cable.

Note: Your actual Internet connection speed depends on the speed of the modem, the router, the Wi-Fi connection, switches, the connected client itself, and the broadband data plan you pay for, whichever is the lowest. Most of the time, what you pay for is the lowest common denominator.

The long answer:A cable modem is the device that receives Internet signal from the cable provider and turns it into a data signal that computing devices, like personal computers,
tablets, or smartphones can understand. A modem comes with a coaxial female connector -- just like the one behind your HDTV -- and a LAN port. This means that with just a modem, you can connect only one computer to the Internet at a time. To connect more devices, you will need to get a Wi-Fi router. (More on this below.)

Modem

Speed per channel

# of channels

Cap Internet speed

DOCSIS 1.x

43Mbps down / 10Mbps up

1 down / 1 up

43Mbps down / 10Mbps up

DOCSIS 2.0

43Mbps down / 31Mbps up

1 down / 1 up

43Mbps down / 31Mbps up

DOCSIS 3.0

43Mbps down / 31Mbps up

4 or 8 down / 4 up

172Mbps or 344Mbps down/ 124Mbps up

Modems are generally very simple devices and because of that most of them are basically the same. The biggest difference between them is the standard they support, which determines the Internet speed capacity, both for download and upload, that they are capable of delivering. This standard is called data over cable service interface specification, or DOCSIS.

Currently, there are DOCSIS 1.x, DOCSIS 2.0, and DOCSIS 3.0 modems on the market. Both DOCSIS 1.x (largely obsolete now) and DOCSIS 2.0 support only a single channel that has a download speed capacity of 43Mbps, and an upload speed cap of 10Mbps and 31Mbps, respectively.

In DOCSIS 3.0 (which is backward-compatible with older standards) the speed capacity of a single channel remains 43Mbps down and 31Mbps up, but the modems are now capable of handling multiple channels (channel bonding) at a time. A typical DOCSIS 3.0 modem generally offers four or eight channels for downloading, resulting in a speed cap of 172Mbps or 344Mbps, respectively. For upload, they generally support four channels to offer a speed of up to 124Mbps. Relatively soon there will be DOCSIS 3.0 modems that can handle even more channels.

Your actual broadband speed at home also depends on what you pay for; the faster you want, the more expensive the monthly cost. If you're paying for a cable Internet plan with a download speed of 30Mbps or less, chances are you'll be fine with a DOCSIS 2.0 modem, which costs almost half the price of its DOCSIS 3.0 counterpart. More specifically, if your cable Internet plan is called Lite, Basic, Starter, Essential, or Standard, you'll probably just need a DOCSIS 2.0 modem, but if you opt for a higher tier, such as a Turbo, Preferred, Premier, Extreme, or Ultimate plan, a DOCSIS 3.0 modem with four or even eight download channels is a must.

Note that all broadband services offer a much slower upload speed than the download speed. Most of the time, for residential broadband plans, the upload speed caps at just 10Mbps. Also, aside from making sure the modem is of the DOCSIS standard, make sure you get one that's on the Internet provider's approved list or else it might not work at all. Also, at least one ISP, Charter, doesn't allow customer-owned modems on its network, so do a little homework before shopping.

In a typical cable-Internet-based home network, you connect the modem to a Wi-Fi router's WAN port using a (preferably) short network cable, to share the Internet connection with multiple devices.

Rent or buy?

The short answer: When possible, it's best to get your own modem. This is a great savings over time.

The long answer: When you sign up for a cable Internet service, the provider often includes a modem (or a combo device -- more on this below) in the package. This device is generally not free, per se; it costs you a monthly rental fee. Oftentimes, the provider doesn't clearly inform you of this charge or that you can avoid it by getting your own equipment. This fee might start as low as a few dollars and then increase to $8 to $10 per month within several months.

That doesn't sounds like a lot, but over time, this adds up to a big chunk of change. And if you plan on using the service for a year or so, it's a much better deal to get your own modem, which costs between $50 and $100, new. You can buy one prior to signing up or any time after that. In the latter case, make sure you return the carrier-provided modem, or else you'll be charged its full price. In my personal experience, it's best to bring that device and return it in person at a local center location to avoid a "lost in the mail" incident.

Even if you plan on using the service for a short time, it's still a good idea to get your own modem. You can likely reuse it for your new service, as long as it's still cable Internet, or sell it and get most of what you've paid for it back.

And speaking of selling your old modem, well, you can buy a used one, too.

New, used, or refurb?

The short answer:
It never hurts to buy a brand-new modem, but you can save a lot, and lose nothing, if you go for a used or refurbished one.

The long answer:Cable modems are simple devices and once set up, they just remain in one place. You never have to change any settings or customize anything at all. There are also no moving parts inside modems (most of them don't even have ventilation fans). For this reason, they can work for a long time and tend to become obsolete before they actually stop working. This means that getting a brand-new modem gives you no more benefits than getting a refurbished one of the same type.

The truth is, most refurbished modems (and networking devices for that matter) are just items returned from buyers for cosmetic reasons or are no longer needed. On the inside, they are the same as a new one. In many cases, the modem that the Internet provider offers to lend you is likely a refurbished model that has been used buy previous customers. On the market, refurbished modems cost up to two thirds of the price of the new unit.

Used modems might come with a little higher risk depending on the previous owners. If the item hasn't been dropped or physically abused, it should work fine. That said, if you buy an used one, make sure you can return it after a few days, because if it can work for a few days without a problem, chances are it will work for a long time. In return, an used modem tends to be just about a third the price of a new one.

In my personal experience, the part of a modem that tends to break down first is the power adapter, which is quite easy to replace.

The back of a cable Internet combo device. Note the multiple LAN ports and the lack of a WAN port found in a typical router.

Should I get a router-modem combo or two separate devices?

The short answer:
Unless the combo device is provided for free (not likely), always get just a standalone modem and a separate router. After getting the modem, just pick up one of the routers on these lists according to your need. If you really want a combo device for practical reasons, such as keeping your home less cluttered with wires, the Motorola SBG6782-AC Surfboard eXtreme is your best bet for now. Make sure you check out its full review first.

The long answer:
As mentioned above, you need a router to share the Internet connection from the cable modem with more than one computer; the total is up to 254 clients for most routers. You just need to connect the modem's LAN port to the router's WAN port using a network cable. This is a preferred setup and also the most popular one, since gives you the flexibility and the options to customize your network based on your need and your budget.

There are also combo devices that include both the modem and the router in a single box. Generally I don't recommend these for two main reasons. First, it's risky. If either part of the device, the modem part or a router part, is broken or becomes obsolete, you have to replace the entire thing. The second reason is in most existing combo devices, the router part is generally very limited, making your home network a lot less capable and flexible than it could be.

If you're running a business, try to avoid a combo device, because the its router part likely won't have all the settings and configuration options needed for your business. A capable administrator can still make it work by getting another router but that's a lot more work than just getting the modem and the right router right off the bat.

Should I buy an extended warranty?

Not at all. Cable modems (or combo devices), even refurbished ones, generally come with a factory warranty ranging from 90 days to a year. Since these are simple devices, if anything unusual should happen, such as if you get a defective unit, you'll run into issues when setting it up or after just a few days of operation. After that, it's likely that nothing will happen.

That said, buying extended warranty is just a waste of money. Instead you should use that money to buy a power surge protector for your home network devices since lighting and power surges are the two most popular causes that damage these equipment. You should also leave the device in an open and dry area to ovoid water damage or overheat.

Also note that if the modem does break down, it's much faster to get a replacement yourself. The warranty process can take days, if not weeks, and during that time, you're offline. So if you really want to make sure you're always connected to the world, get a second (used) modem as spare.

Should I try to bargain?

Definitely.

It's true that most of us live in an area that's served by just one cable company, but there are other alternatives, such as FIOS, satellite, or DSL (which is ubiquitous and generally cheaper). You should use these as your leverage with the cable company for a better deal. You can also get deals by subscribing to multiple-service packages, such as TV, Internet, and phone, though don't subscribe for what you're not planning on using.

Some cable companies, such as Comcast, tend to give you good rates for a promotional period, say six months, and then start charging you the full rate, which is up to 50 percent higher. You can always call in when this period ends and ask for another promotional period, or you can just quit and resubscribe. This doesn't cost anything, and you already have the modem.

Most importantly, check with them once in a while when there are new promotions, or just simply call in to ask for a lower rates. It works. After all, you can't get what you don't ask for.

That's it for now. If you have more questions or tips, send them my way via Facebook, Twitter, or Google+, or just share them in the comments section below.